MYTH AND FACT

There are endless food myths parents use every day to get their children to eat nutritious food – 'spinach will make you strong like Popeye', 'an apple a day keeps the doctor away' and 'eating carrots helps you see in the dark'.

A major Australian study called the Blue Mountains eye study, conducted in the late 1990s, examined the link between increased vitamin A intake and deteriorating night vision in older people. The authors found that people who reported having poor eyesight ate more carrots – just as their mothers had told them – to improve their eyesight. But it didn't help.

While there is some truth to the old wives' tale regarding carrots and eyesight, Professor Algis Vingrys, from the University of Melbourne's Department of Optometry and Vision Services, says no amount of carrots will improve your eyesight if you already have a well balanced diet.

A diet with sufficient vitamin A, iron and other provitamins (substances that our bodies can convert into vitamins) is vital for eye health.

There are two types of vitamin A: retinoids and carotenoids.

Retinoids are a lipid form of vitamin A found in liver, fish oils containing liver (eg cod-liver oil) and butter. Eating large amounts of these substances can give you an overdose of vitamin A and lead to toxicity, or worse, promote some forms of cancer.

Carotenoids are provitamins your body converts into vitamin A. Carrots, broccoli, sweet potatoes, pumpkin and dark-green leafy vegetables all contain beta-carotene, a potent carotenoid. But how much gets converted depends on how much vitamin A you already have in your body – in other words, your body doesn't make vitamin A if you don't need it.

A diet deficient in vitamin A can lead to night blindness and other eye problems. Reduced night vision is one of the earliest signs of vitamin A deficiency although people rarely complain of night blindness until it becomes really severe.

But vitamin A deficiency is rare in Australia. Most of us eat a reasonably balanced diet, although pregnant women, those who don't eat a varied nutritious diet and some people with bowel disease may need to see their doctor if they feel they are at risk.

Eating carrots (and other sources of vitamin A) can improve night vision if you are deficient in vitamin A, (you also need to be getting enough zinc and iron) but not if you already have a balanced diet.

The vision loss reported by the people in the Blue Mountains eye study was caused by age-related deterioration not a dietary deficiency, which is why their eyesight didn't improve regardless of how many carrots they chomped on.